Automated vs Manual Coverage on a Blade Bond Line

The dimensions that decide

Which way the call goes

The evidence is the part that decides. A manual pass leaves a route and a set of readings, and it cannot show what it did not scan. An automated pass leaves a map indexed at plus or minus 0.1 mm against the blade model, so a gap in coverage is visible as a gap rather than invisible as a clean result. With 15-25 % operator variation on a manual reading, the record of the pass varies with who held the probe, while the automated map is the same artefact every campaign. That is what an auditor reviewing 100 % of the primary bond lines is looking for.

How to choose between them

Run these checks in order. By Step 5 the choice follows from the geometry and the threshold rather than from habit.

1. Fix the acceptance threshold. Start from the threshold the zone carries, not from the method you happen to own. IEC 61400-5 Section 11 asks for volumetric detection of indications 6 mm and larger in the laminate plane, and DNV-ST-0126 tightens the leading edge to 3 mm, so the threshold is set before the probe is chosen.
2. Read the geometry off the drawing. Measure the thickness and the curvature the probe has to travel. A spar cap up to 80 mm of unidirectional laminate and a root transition of changing radius are two different scan problems, and the radius decides how the array is coupled.
3. Choose the modality pair. Pick modules by defect geometry, not by habit. PAUT images planar separations that lie parallel to the plies, TOFD catches volumetric clusters whatever their orientation, and running both on a 256-channel system puts the two mechanisms in one pass.
4. Automate the scan path. Put the probe on an encoder-driven carriage and let the path, not the technician, set coverage. A 600 mm spar cap falls to one longitudinal pass at 500 mm/s on a linear array, where a single-element probe needs 20 parallel passes and runs about five times longer.
5. Lock the evidence chain. Write the coverage map, the daily calibration and the indication log to the blade serial while the scan is running. It is the difference between a 3-day type-certification audit and a 3-hour document review, and it is what ISO 9712 qualification is there to sign.

These are the working numbers from our own machine and campaign records, restated rather than re-pitched.